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8-PORT SERIAL HOST ADAPTER PCI
Appendix B: RS-232 Electrical
Interface
The most widely used communication standard is RS-232. It’s been defined and
revised several times and is sometimes also called EIA/TIA-232. The IBM AT
computer defined the RS-232 port on a DB9 connector, and subsequently the
EIA/TIA approved this implementation as the EIA/TIA-574 standard, which is
defined as the “9-Position Non-Synchronous Interface between Data Terminal
Equipment and Data Circuit-Terminating Equipment Employing Serial Binary
Data Interchange.”
RS-232 can operate at data rates of up to 20 kbps at distances less than 50 ft.
(15.2 m). The absolute maximum data rate may vary depending on line conditions
and cable lengths. RS-232 is a single-ended or unbalanced interface, meaning that
a single electrical signal is compared to a common signal (ground) to determine
binary logical states. The RS-232 and the EIA/TIA-574 specification define two
types of interface circuits, Data Terminal Equipment (DTE) and Data Circuit-
Terminating Equipment (DCE). The Serial Host Adapter is a DTE device.